What is the molarity of a solution if 80 grams of NaOH (molar mass = 40 g/mol) are dissolved in 500 mL of water?
Understand the Problem
The question is asking to calculate the molarity of a sodium hydroxide (NaOH) solution. We are given the mass of NaOH (80 grams), its molar mass (40 g/mol), and the volume of the solution (500 mL). To find the molarity, we need to calculate the number of moles of NaOH and then divide by the volume of the solution in liters.
Answer
The molarity of the sodium hydroxide solution is $4 \, M$.
Answer for screen readers
The molarity of the sodium hydroxide solution is $4 , M$.
Steps to Solve
- Calculate the number of moles of NaOH
To find the number of moles, divide the given mass of NaOH by its molar mass:
$moles = \frac{mass}{molar mass}$ $moles = \frac{80 , g}{40 , g/mol} = 2 , mol$
- Convert the volume of the solution from milliliters to liters
Since molarity is defined as moles per liter, we need to convert the volume from mL to L:
$Volume , (L) = \frac{Volume , (mL)}{1000}$ $Volume , (L) = \frac{500 , mL}{1000} = 0.5 , L$
- Calculate the molarity of the NaOH solution
Molarity is defined as the number of moles of solute divided by the volume of the solution in liters:
$Molarity = \frac{moles , of , solute}{Volume , of , solution , (L)}$ $Molarity = \frac{2 , mol}{0.5 , L} = 4 , M$
The molarity of the sodium hydroxide solution is $4 , M$.
More Information
Molarity is a common unit of concentration in chemistry, representing the number of moles of solute per liter of solution. It is temperature-dependent, as the volume of a solution changes with temperature.
Tips
A common mistake is forgetting to convert the volume from milliliters to liters before calculating the molarity. Another mistake is using the wrong formula to calculate the number of moles, perhaps dividing the molar mass by the mass instead of mass by molar mass.
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